A liquid crystal display device can display an image by means of optical anisotropy and dual-refraction of liquid crystal molecules. In a display panel of the liquid crystal display device, two transparent insulation substrates are opposite to each other, and electrodes for generating an electric field are formed on the substrates opposite to each other, and liquid crystal are injected between the two substrates. Subsequently, a voltage is applied to the electrodes on the substrates so as to generate an electric field for changing arrangement direction of liquid crystal molecules. Thus, the amount of light transmitted through the transparent insulation substrates can be controlled, and desired images to be displayed can be obtained. Generally, because the liquid crystal display device with the above structure includes thin film transistors (TFTs) as switches, it is also referred to as thin film transistor liquid crystal display (TFT-LCD).
FIG. 1 shows a perspective diagram of a conventional liquid crystal display panel. As illustrated in FIG. 1, the liquid crystal display panel in the liquid crystal display device includes an upper substrate 50 and a lower substrate 70 adhered to each other by means of a frame adhesive (not shown). There is a predetermined space between the upper substrate 50 and the lower substrate 70. The liquid crystal layer 60 is injected into the space. A plurality of scanning lines 73 and a plurality of data lines 72 are disposed on a transparent glass substrate 71 of the lower substrate 70. The plurality of scanning lines 73 are arranged along one direction with a predetermined distance, and the plurality of data lines 72 are arranged along a direction perpendicular to the scanning lines 73, so that the pixel region (pixel) 75 is defined. The pixel electrode 74 is formed on the pixel region 75. Thin film transistors (TFTs) Q are formed at intercross locations of the scanning lines 73 and the date lines 72. The TFT applies a data signal of data lines 72 to the pixel electrode 74 through a scanning signal applied from scanning lines 73.
A black matrix layer 52 for shielding the light outside the pixel region 75, which is also referred to as a black bottom layer, is formed on the transparent glass substrate 51 of the upper substrate 50. Red (R), green (G) and blue (B) color filter layers for different colors are formed on a region of the upper substrate corresponding to the pixel region. A common electrode layer 54 is formed on the color filter layer 53 for driving the liquid crystal to display images.
In order to inject the liquid crystal between the upper substrate and the lower substrate, a supporter is configured between the upper substrate and the lower substrate to provide a required cell gap. The supporter is generally referred to as a spacer and is disposed above the data lines and the scanning lines to only provide a space to prevent the upper substrate and the lower substrate from contacting, without influence on the image displaying. The material of the spacer commonly includes a photosensitive resin such as acrylic resin. The shape of the spacer may be spheroid, column and trapezoid formed by the photolithography process. FIG. 2 is a planar schematic diagram of a liquid crystal display panel illustrating arrangement of a spacer. As illustrated in FIG. 2, data lines 11, scanning lines 12 and TFT including an active layer 13, a source electrode 14 and a drain electrode 15 are disposed within a region defined by the black matrix layer 25. The drain electrode 15 is connected to a pixel electrode 10 via a through hole 16 and a spacer 30 is formed above the scanning lines 12. FIG. 2a is a cross-sectional diagram of the spacer of FIG. 2 taken along line A-A′. As illustrated in FIG. 2a, the scanning lines 12 are formed on a glass substrate 1 of the lower substrate. A gate insulation layer 3 and a passivation layer 4 are formed in sequence on the glass substrate 1 and the scanning lines 12. The black matrix layer 25 and a light color filter layer 21 are formed on a glass substrate 2 of the upper substrate, and the spacer 30 is formed on a common electrode. A pixel electrode 10 is formed on the passivation layer 4 and corresponds to a position of the light color filter layer 21. The height of the spacer 30 is suitable for contacting with the passivation layer 4, after the upper substrate and the lower substrate are adhered by the frame adhesive.
However, in the case of that an external force in a transverse or an oblique direction is applied to the liquid crystal display panel, as illustrated in FIG. 2b, the spacer 30 is offset and can not return to its original position. In particular, when the distribution density of the spacers 30 is large, it is more difficult to make all the spacers return to their original position. Thus, the so-called Push Mura is caused. That is, the patterns of the upper substrate and the lower substrate are not aligned, and a light leakage region is occurred as indicated in dash line A1, thus the normal display for images is influenced. Not only the position but also the distribution density of the spacers have an effect on the quality of display. For example, when the distribution density of the spacers is too large, the amount of compression of the spacer is decreased. Because thermal expansion coefficients of the spacer and the liquid crystal are different, the thickness of the liquid crystal layer can not be controlled. Particularly, in the case of low temperature, the low-temperature bubbles are generated. When the liquid crystal display panel is placed perpendicularly, the liquid crystals may accumulate at a bottom of the liquid crystal display panel and the non-uniformity illumination is caused. Thus, the phenomenon of bottom expansion (also referred to as the Gravity Mura) is occurred.
On the other hand, if the distribution density of the column-shaped spacers is too small, the liquid crystal display panel can not have enough mechanical strength. When a pressure force is applied to the liquid crystal display panel perpendicularly, the cell gap changes because the liquid crystal display panel is pressed. The phenomenon of non-uniformity cell gap is occurred (hereinafter, referred to as the Press Mura). Therefore, it is necessary to arrange the column-shaped spacers with a suitable density.
FIG. 3 is a planar schematic diagram of another liquid crystal display panel illustrating arrangement for spacers. As illustrated in FIG. 3, two types of spacers are disposed on the liquid crystal display panel. The first spacer 30 and the second spacer 30′ are respectively disposed above the scanning lines 12 with a certain ratio. FIG. 3a is cross-sectional diagram of the first spacer 30 of FIG. 3 taken along line B-B′. As illustrated in FIG. 3a, a dielectric layer 130 and a metal layer 40 are added on the scanning lines 12 corresponding to the first spacer 30. When the upper substrate and the lower substrate are vacuum sealed, the first spacer 30 may be pressed. Thus, the function of segregating and sealing the liquid crystal can be improved. In addition, when the liquid crystal display panel is placed perpendicularly, the liquid crystal can be prevented from accumulating at the bottom of the liquid crystal display panel. Thus, the Gravity Mura is alleviated. FIG. 3b is cross-sectional diagram of the second spacer 30′ of FIG. 3 taken along line C-C′. As illustrated in FIG. 3b, the insulating layer 3 and the passivation layer 4 are configured on the scanning lines 12. A gap occurs between the second spacer 30′ and the passivation layer 4 after the upper substrate and the lower substrate are vacuum sealed. When an external force is applied to the liquid crystal display panel, the upper substrate elasticly contacts the lower substrate, so that the phenomenon of the Press Mura can be reduced to a certain extent.
However, as can be known from the above analysis, when an external force in a transverse or a lateral direction is applied to the liquid crystal display panel, the spacer may still be moved. Therefore, it is inevitable that the phenomenon of the Push Mura occurs.